Buggy code:
public class CreateClosedCompetitionGroupFragment extends EventFragment { View view_container ; private boolean success = false ; private ProgressDialog pdialog ; String courses_json ; TextView date_view ; TextView date_view2 ; TableLayout competitor_list ; String retVal ; private List < UserModel > listUser = new ArrayList < UserModel > ( ) ; private GroupMemberAdapter listAdapter ; @ InjectView ( id . competitor_container ) LinearLayout btnAddMember ; @ InjectView ( id . lv_competition_create_group_addmember ) ListView listView ; private View view ; private final String createGroupQueue = "CreateGroupQueue" ; private class Courses { int id = 0 ; String course = "" ; public Courses ( int _id , String _course ) { } public String toString ( ) { } } private class InitLists extends AsyncTask < String , String , String > { public InitLists ( ) { } @ Override protected void onPreExecute ( ) { } @ Override protected String doInBackground ( String ... strings ) { } @ Override protected void onPostExecute ( String result ) { } } private class CompetitionCreate extends AsyncTask < String , String , String > { StringBuilder text = new StringBuilder ( ) ; public CompetitionCreate ( ) { } @ Override protected void onPreExecute ( ) { } @ Override protected String doInBackground ( String ... strings ) { } @ Override protected void onPostExecute ( String result ) { } } @ Override public View onCreateView ( LayoutInflater inflater , ViewGroup container , Bundle savedInstanceState ) { } @ Override public void onViewCreated ( View view , Bundle savedInstanceState ) { } private void CreateGroup ( String groupName , String competition ) { String urlString = ( ( ( Api . WEB_URL ) + "closed-competition//" ) + competition ) + "//create-group" ; final ProgressDialog pDialog = new ProgressDialog ( getActivity ( ) ) ; pDialog . setMessage ( getResources ( ) . getString ( jap_registering ) ) ; pDialog . show ( ) ; JSONObject requestObject = new JSONObject ( ) ; try { requestObject . put ( "name" , groupName ) ; JSONArray arr = new JSONArray ( generateMemberArray ( ) ) ; requestObject . put ( "members" , arr ) ; } catch ( JSONException e ) { e . printStackTrace ( ) ; } Log . d ( TAG , urlString ) ; JsonObjectRequest jsonObjReq = new JsonObjectRequest ( Method . POST , urlString , requestObject , new Response . Listener < JSONObject > ( ) { @ Override public void onResponse ( JSONObject response ) { pDialog . dismiss ( ) ; Toast . makeText ( getActivity ( ) , getResources ( ) . getString ( R . string . jap_reg_success ) , Toast . LENGTH_SHORT ) . show ( ) ; } } , new Response . ErrorListener ( ) { @ Override public void onErrorResponse ( VolleyError error ) { VolleyLog . d ( TAG , error . getLocalizedMessage ( ) ) ; pDialog . dismiss ( ) ; if ( String . valueOf ( error . networkResponse . statusCode ) . equals ( "500" ) ) { <START_BUG> Toast . makeText ( getActivity ( ) , "プレイヤーが重複しています。ご確認ください。" , LENGTH_SHORT ) . show ( ) ; <END_BUG> } else { Toast . makeText ( getActivity ( ) , getResources ( ) . getString ( jap_something_wrong ) , LENGTH_SHORT ) . show ( ) ; } } } ) { @ Override public Map < String , String > getHeaders ( ) throws AuthFailureError { Map < String , String > headers = super . getHeaders ( ) ; if ( ( headers == null ) || ( headers . equals ( Collections . emptyMap ( ) ) ) ) { headers = new HashMap < String , String > ( ) ; } headers . put ( AUTHORIZATION , ( ( Api . BEARER ) + ( Api . getToken ( getActivity ( ) ) ) ) ) ; return headers ; } } ; GolfApp . addToRequestQueue ( jsonObjReq , createGroupQueue ) ; } private List < String > generateMemberArray ( ) { } @ OnClick ( id . competitor_container ) public void callAddMember ( ) { } public void onEvent ( UserModel userModel ) { } }

Fix:
Toast . makeText ( getActivity ( ) , "メンバーはすでに競争の中で、別のグループに参加している。" , LENGTH_SHORT ) . show ( ) ;